Nah without question. Her starting skillset is absolutely horrid, so she's dependent on her dad for her entire skillset. While Gaius, Gregor, and The Vaike give her some good stuff, she'll always be short a few important skills without MU's help. It's also the only way to maximize the Galeforce+Luna combo among the kids.
Of course, this comes with the drawback of having to marry Nowi, so I can never stomach doing this pairing myself... Noire and Owain are probably the next best candidates if you don't go with Nah.
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